A wild hack at making [jpegtran](http://jpegclub.org/jpegtran/) white-pad images when extending them, instead of using middle gray

gistfile1.darcspatch

--- transupp.c.orig 2015-03-16 11:34:25.000000000 -0600
+++ transupp.c  2015-03-16 11:39:12.000000000 -0600
@@ -130,6 +130,9 @@
   JBLOCKARRAY src_buffer, dst_buffer;
   jpeg_component_info *compptr;
 
+  JCOEF pad = 1023; /* max for 8-bit JPEG = white; use 16383 for 12-bit JPEG */
+  int pio, pii;     /* padding indices for custom FMEMZERO() replacments */
+
   MCU_cols = srcinfo->output_width /
     (dstinfo->max_h_samp_factor * dstinfo->min_DCT_h_scaled_size);
   MCU_rows = srcinfo->output_height /
@@ -150,8 +153,11 @@
    if (dst_blk_y < y_crop_blocks ||
        dst_blk_y >= comp_height + y_crop_blocks) {
      for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
-       FMEMZERO(dst_buffer[offset_y],
-            compptr->width_in_blocks * SIZEOF(JBLOCK));
+       for (pio = 0; pio < compptr->width_in_blocks; ++pio) {
+         for (pii = 0; pio < SIZEOF(JBLOCK); ++pii) {
+           dst_buffer[offset_y][pio][pii] = pad;
+         }
+       }
      }
      continue;
    }
@@ -168,17 +174,22 @@
       for (offset_y = 0; offset_y < compptr->v_samp_factor; offset_y++) {
    if (dstinfo->jpeg_width > srcinfo->output_width) {
      if (x_crop_blocks > 0) {
-       FMEMZERO(dst_buffer[offset_y],
-            x_crop_blocks * SIZEOF(JBLOCK));
+       for (pio = 0; pio < x_crop_blocks; ++pio) {
+         for (pii = 0; pio < SIZEOF(JBLOCK); ++pii) {
+           dst_buffer[offset_y][pio][pii] = pad;
+         }
+       }
      }
      jcopy_block_row(src_buffer[offset_y],
              dst_buffer[offset_y] + x_crop_blocks,
              comp_width);
      if (compptr->width_in_blocks > comp_width + x_crop_blocks) {
-       FMEMZERO(dst_buffer[offset_y] +
-              comp_width + x_crop_blocks,
-            (compptr->width_in_blocks -
-              comp_width - x_crop_blocks) * SIZEOF(JBLOCK));
+       int count = compptr->width_in_blocks - comp_width - x_crop_blocks;
+       for (pio = 0; pio < count; ++pio) {
+         for (pii = 0; pio < SIZEOF(JBLOCK); ++pii) {
+           dst_buffer[offset_y][pio + comp_width + x_crop_blocks][pii] = pad;
+         }
+       }
      }
    } else {
      jcopy_block_row(src_buffer[offset_y] + x_crop_blocks,